Re: Lilypond Substitution Function

On Sat, Feb 27, 2021 at 10:43 AM Jean Abou Samra <jean@abou-samra.fr> wrote:

Le 27/02/2021 à 02:16, Ken Ledeen a écrit :

> I am struggling to understand the restrictions on substitution functions.
>
> For example:
>
> 1) can a function include "\score { ...}" or can it only be invoked
> INSIDE a \score?
>
> 2) is it possible to include \header { ...} inside a substitution
> function? It fails when I try, but I don't understand why.
>
> I assume I am missing some basic concepts regarding their use.
>
> Thanks!

Hello,

Music functions must return music objects; \score blocks are not music
but general containers that enclose music as well as other objects such
as \header and \layout blocks.

However, replacing define-music-function with define-scheme-function,
you can define more versatile functions that are allowed to return any
kind of object for interpretation. For example:

\version "2.23.1"

failingFunction =
#(define-music-function () ()
    #{
      \score {
        \header {
          piece = "Piece A"
        }
        { c' }
      }
    #})

% \failingFunction

succeedingFunction =
#(define-scheme-function () ()
    #{
      \score {
        \header {
          piece = "Piece B"
        }
        { c' }
      }
    #})

\succeedingFunction

Hope that helps,
Jean

From:	Ken Ledeen
Subject:	Re: Lilypond Substitution Function
Date:	Sat, 27 Feb 2021 10:49:36 -0500